The present invention relates generally to scintillator compositions and related structures and methods. More specifically, the present invention relates to lanthanum halide scintillator compositions and methods of fabricating scintillator compositions using evaporation-based techniques.
Scintillation spectrometers are widely used in detection and spectroscopy of energetic photons (e.g., X-rays and γ-rays). Such detectors are commonly used, for example, in nuclear and particle physics research, medical imaging, diffraction, non destructive testing, nuclear treaty verification and safeguards, nuclear non-proliferation monitoring, and geological exploration.
Important requirements for the scintillation materials used in these applications include high light output, transparency to the light it produces, high stopping efficiency, fast response, good proportionality, low cost and availability in large volume. These requirements are often not met by many of the commercially available scintillators. While general classes of chemical compositions may be identified as potentially having some attractive scintillation characteristic(s), specific compositions/formulations and structures having both scintillation characteristics and physical properties necessary for actual use in scintillation spectrometers and various practical applications, as well as capability of imaging at a high resolution, have proven difficult to predict or produce. Specific scintillation properties are not necessarily predictable from chemical composition alone, and preparing effective scintillators from even candidate materials often proves difficult. For example, while the composition of sodium chloride had been known for many years, the invention by Hofstadter of a high light-yield and conversion efficiency scintillator from sodium iodide doped with thallium launched the era of modern radiation spectrometry. More than half a century later, thallium doped sodium iodide, in fact, still remains one of the most widely used scintillator materials. Since the invention of NaI(T1) scintillators in the 1940's, for half a century radiation detection applications have depended to a significant extent on this material. As the methodology of scintillator development evolved, new materials have been added, and yet, specific applications, particularly those requiring high resolution imaging and large volumes, are still hampered by the lack of scintillators suitable for particular applications.
As a result, there is continued interest in the search for new scintillator formulations and physical structures with both the enhanced performance and the physical characteristics needed for use in various applications. Today, the development of new scintillators continues to be as much an art as a science, since the composition of a given material does not necessarily determine its performance and structural properties as a scintillator, which are strongly influenced by the history (e.g., fabrication process) of the material as it is formed. While it is may be possible to reject a potential scintillator for a specific application based solely on composition, it is not possible to predict whether a material with promising composition will produce a scintillator with the desired properties.
One promising group of scintillator compositions includes those made of lanthanum halides. Solid crystalline forms of cerium (Ce) doped LaBr have been produced and currently available from commercial sources. For example, bulk LaBr crystals have been synthesized by melt-based techniques and using crystal growth techniques such as though the high pressure Bridgman technique to successfully produce scintillation grade material. Crystal growth methods as above, however, are generally complex, require specialized equipment, and extreme care to obtain a defect-free crystal growth. The complexity of the current methods often results in yield problems and a high cost for the scintillator.
Crystalline LaBr3 films have also been fabricated by epitaxial growth techniques. However, the process has generally been expensive and produced generally thin films. Given the promising scintillation characteristics of crystalline LaBr3 materials, fabrication of larger scintillators is a cost-efficient manner would be tremendously beneficial.
Thus, a need exists for improved scintillator compositions and structures, including improved lanthanum halide scintillators, suitable for use in various radiation detection applications, as well as improved methods of fabricating larger scale scintillator films is a more cost-effective manner.